Our multifaceted investigation of normal and atypical melanocytes will continued with major emphasis on the following topics: A. Characterization of the sites of hormonal and neural control in pigment cells through adenylcyclase and phosphodiesterase activities and the relationship of these control sites to alpha and beta adrenergic receptors. B. Isolation of MSH-receptor molecules from malignant melanocytes. C. Examination of the viral-like structures in melanomas. D. Isolation and analysis of mutant melanocytes defective in normal phenotypic expression. E. Mechanism of tyrosinase activation. F. Study of the fine structure during transfer of melanin from melanocytes to keratinocytes. G. Ultranstructural localization of tyrosinase, adenylcyclase, and acetylcholinesterase in melanocytes.